1. Technical Field
The present invention relates to a waveguide coupler, and more particularly, to a 3-D waveguide coupling device capable of two-step coupling, which has at least one 3-D tapered structure layer, at least one coupling material layer and at least one assisting grating, so that light is able to be coupled into a waveguide layer through the 3-D tapered structure layer, the coupling material layer and the assisting grating by way of two-step coupling.
2. Description of Related Art
Optical devices can be divided into active devices and passive devices, the active device indicates that the optical device capable of generation or amplification of light, or absorption of light into electronic signals; and the passive device represents that the optical device showing the ability of optical signal processing in time or frequency domains.
A coupler is a passive optical device used for optical power transfer between two optical media, for example: between two waveguide couplers or between a fiber and a waveguide coupler. With the development of the semiconductor manufacturing technology, an integrated coupler is able to be fabricated by way of thin film deposition, photolithography and etching processes. Moreover, a grating structure can be formed on a waveguide layer, so as to assist power transfer between the optical medium and the waveguide coupler with the aid of phase matching induced by the grating. Such a grating coupler is able to increase the efficiency of light coupling by adjusting the arrangement period of the grating.
However, when using the abovementioned grating-assisting waveguide coupler to transform the light energy from one optical medium to another, for example, a fiber to a waveguide coupler, the effective energy transformation is critical and limited by the alignment angle between the waveguide coupler and fiber. An easy way is to put the fiber and waveguide coupler in parallel and to take advantage of evanescent coupling. However, due to the size difference between these two elements, the coupling efficiency is very low, in additions, the height of the waveguide coupler is constrained by the semiconductor thin film process and can not be fabricated to be very high, so as to cause the difficulty for optical connection between the waveguide coupler and the fiber through the grating structure.
In view of the drawbacks and shortcomings of conventional grating couplers, inventors do researches hardly and expect to improve the disadvantages of the grating couplers described above. A grating-assisting three dimension waveguide couple device and a method for manufacturing thereof were disclosed in a R.O.C patent with patent application number 98,136,872, referring to FIGS. 1A and 1B, which illustrate a stereo view and a cross-section view of the grating-assisting three dimension waveguide couple device, respectively, where the grating-assisting three dimension waveguide couple device 1a includes: a first substrate 11a, which is a silicon-on-insulator (SOI) substrate with a semiconductor 111a and a insulator 112a; a waveguide layer 12a formed on the first substrate 11a and as a propagation layer of the light; an assisting grating 4a formed on the waveguide layer 12a and capable of help to lead the light into the waveguide layer 12a by way of phase match; and a plurality of 3-D tapered structure layer 19a formed on the waveguide layer 12a and cover the assisting grating 4a, moreover, there is a height differential being existed between the two sides of the 3-D tapered structure layer 19a, so as to make a two-dimension transverse variation of the 3-D tapered structure layer 19a; So that, the two-dimension transverse variation the utility of the assisting grating 4a produce the coincidence of the propagation constants of the 3-D tapered structure layer 19a and the waveguide layer 12a, so as to increase the coupling efficiency of both things, then the light can be efficiently transferred into the waveguide layer 12a from the 3-D tapered structure layer 19a when the light is propagated in the 3-D tapered structure layer 19a, therefore, the energy coupling efficiency of light between two optical media is increased.
Concerning the practicable application of the grating-assist three dimension waveguide couple device 1a, the refractive index of the 3-D tapered structure layer 19a may be very different from refractive index of the waveguide layer 12a. Although the two-dimension transverse variation the utility of the assisting grating 4a produce the coincidence of the propagation constants of the 3-D tapered structure layer 19a and the waveguide layer 12a so as to increase the coupling efficiency of both things, a considerable degree of scattering loss is produced when the light pass through the assisting grating 4a. So that the coupling efficiency of the grating-assist three dimension waveguide couple device 1a is still need to be improved.
Accordingly, in view of the drawbacks and shortcomings of the grating-assisting waveguide and the grating-assist three dimension waveguide couple device, the inventor of the present application has made great efforts to make inventive research thereon and eventually provided a 3-D waveguide coupling device capable of two-step coupling and a manufacture method thereof according to the present invention.